1. Field of the Invention
This invention relates to a seal for the piston rod of a Stirling engine and, more particularly, to a piston rod seal adapted to forcibly return to a fluid-filled chamber a fluid which has leaked into an intermediate chamber.
2. Description of the Prior Art
In a Stirling engine, the interior of a cylinder is partitioned by a working piston into an expansion chamber consituting a high-temperature section, and a compression chamber defining a low-temperature section. A working gas is made to move back and forth between the expansion chamber and the compression chamber of a neighboring cylinder, thus to reciprocate the working piston. Motive power is taken off from the engine through a rod connected to the piston. The piston rod is in turn connected to a guide piston which operates in association with a power take-off, or PTO, mechanism. The guide piston is situated on a crank case or swash plate chamber side which is at atmospheric pressure, and the portion at which the piston rod and working piston are connected is situated on the compression side, which is at high pressure. As a result, a pressure differential develops across the piston rod-working piston junction, so that the working gas tends to leak from the high-pressure compression chamber into the lower pressure drive section, such as the crankcase. Since the output of the Stirling engine is proportional to the mean pressure of the working gas, leakage of the working gas from the compression chamber to, e.g., the crankcase must be dealt with in order to prevent a drop it engine output.
More specifically, in the conventional Stirling engine, a gas seal, an intermediate chamber held at the minimum pressure of the working gas, an oil scraper, a fluid filled chamber and an oil seal are disposed between the cylinder and crankcase in order to seal the piston rod. During reciprocation of the piston rod, however, the fluid which flows into the intermediate chamber while adhering to the piston rod is impossible to impede with the oil scraper. Although the fluid which thus flows into the intermediate chamber while adhering to the piston rod may not seem to pose a practical problem, there is the danger that the fluid may build up within the intermediate chamber with time. It is therefore desirable to have some means for removing the fluid in a more positive manner.
Another problem in Stirling engines is a drop in heat exchange efficiency and, hence, a decline in engine output, brought about when lubricating oil for the piston rod flows into the compression chamber, mixes with the working gas and adheres itself to the Stirling engine regenerator.